High blood pressure is a major public health problem worldwide leading to cardiovascular disease and death. The kidneys play a critical role in maintaining normal blood pressure by increasing salt excretion when dietary intake is elevated. Inappropriate salt retention by the kidneys results in hypertension. Understanding the mechanisms by which the kidneys eliminate excess salt will clarify the causes of hypertension and identify new approaches for treatment, extending patient's lives and improving their quality of life. Recent studies have shown that high salt intake increases production of the small peptide endothelin-1 within the kidney; however, its role in stimulating salt excretion in vivo is unknown. The overall goal of this proposal is to investigate how endothelin-1 causes the kidney to eliminate more salt during high salt feeding. Overall hypotheses to be tested are: 1) when dietary salt is elevated, endothelin-1 derived from the nephron acts as an autacoid, inhibiting salt reabsorption and promoting natriuresis; and 2) endothelin-1 also functions as a paracrine factor that acts on adjacent medullary interstitial cells to stimulate medullary blood flow and facilitate sodium excretion. Both mechanisms are crucial for high salt-induced natriuresis, and defects in this system will lead to salt retention and hypertension. These hypotheses will be tested using animals in which expression of individual genes is eliminated only in certain types of cells in the kidney, employing novel approaches that combine in vivo and in vitro technology. This application provides the foundation for a career development plan for Dr. Marcela Herrera, a cell/physiology-trained post-doctoral fellow committed to a research career in kidney disease and hypertension. The applicant will be mentored by Dr. Thomas Coffman at Duke University Medical Center, who will train the PI in generating transgenic animal models and using in vivo physiological techniques to study them. This proposal has been structured to provide complementary and substantive training opportunities. The applicant will gain expertise in mouse genetics, producing transgenic animals, and in vivo physiology. This will provide a solid basis for the trainee to develop a multi-disciplinary program of research using physiological, cellular/molecular, and genetic techniques to achieve her goal of becoming an independent investigator.